trusty: Don't break nop loop on failed custom nop-calls

The SMC_NC_VDEV_KICK_VQ nop handler in trusty sometimes returns an error
early in the boot process. If this happends during an interrupted nop
call, then it would break the loop and leave the trusty cpu in the
interrupted state.

Bug: 145619829
Change-Id: Id5e5439db4623f5017ac9a5100e05ae2519650c6
Signed-off-by: Arve Hjønnevåg <arve@android.com>